Well, first the obvious: seeing Rowan Atkinson in a serious role is kind of difficult at first. But you get used to it, and Rowan shows he is not just Mr. Bean.
Regarding the movie itself: getting a known character from a book series is quite hard. If one can try to find an actor that suites the role, I think that it was not the case. As one of the books of Maigret shows, “Maigret” is not “magro” (thin), but rather a little fat. That is not true with Atkinson performing the character. The second things I miss, is that Maigret, from the books, has a special kind of humor (can’t say dark humor, but a subtle form of humor) and, in this movie, Atkinson has so much fear to be funny that Maigret ends out as a sad policeman, a thing that is not really what is presented on the original books.